1. Field of the Invention (Technical Field)
The present invention relates to a quartz resonator and its support structure and more particularly to a hermetically sealed quartz resonator having a micro-machined support structure.
2. Description of the Prior Art
Quartz resonators are used for oscillators or sensing devices. In particular, a quartz resonator can be used as an oscillator for a watch or any other application which requires small size, low cost and ruggedness. The quartz resonator might also be used for microprocessor applications. A quartz resonator operates by resonating in response to a stimulus, which may be a physical event, such as acceleration or force or pressure, or an electrical signal. In the former usage, the resonator acts as a transducer, and in the latter case, the resonator acts as a frequency source.
Previous technology for resonator support structures is varied and includes features which minimize the effects tending to restrict motion of the resonating surface resulting from physically holding the vibrating resonator body. To this end, the support is usually placed at a vibrational node of the resonator body. With discs operating in radial extension modes, attachment at the center of the disc is a conventional technique for support.
For shear mode type resonators with little vibrational motion normal to the plane of the resonator, conventional support techniques have included various elastic clamping means at the periphery of the resonator where relative shear-motion quiescence occurs. These clamps have conventionally been wires, metallic ribbons, metallic springs, etc. Another conventional support technique has been to fashion the resonator and the resonator support from a single piece of quartz by chemical or mechanical machining methods.
U.S. Pat. No. 4,362,961 to Gerber discloses an encapsulated piezoelectric resonator device wherein a vibrating member and a frame member are formed integrally on a single substrate. The frame/resonator member is sandwiched between and bonded to two cover members which are positioned above and below the resonator member, respectively. The resonator member is connected to a number of electrodes and connection to the electrodes is provided by passages through the two cover members. This resonator operates in a flexure mode. The resonator member and the cover members are rigidly fixed together.
U.S. Pat. No. 4,234,811 to Hishida et al. discloses a supporting structure for a thickness-shear type crystal oscillator for watches wherein the supporting structure of a resonator element has a pair of flexible tongues to support the resonator element from both the top and the bottom of the resonator element. Additionally, another set of tongues is provided to engage notches on the resonator element's periphery to prevent lateral motion.
U.S. Pat. No. 3,988,621 to Nakayama et al. discloses an insulating ring with projections for supporting and rigidly clamping a quartz resonator. Electrodes are placed directly onto the shear-mode resonator and small wires electrically connect the electrodes to the insulating ring.
U.S. Pat. No. 2,002,167 to Beckmann discloses a crystal quartz resonator wherein capacitive coupling is used to excite the resonator. A support for the resonator is disclosed which uses notches and pins on the edge of the resonator.
U.S. Pat. No. 2,161,980 to Runge et al. discloses an elastically oscillating oscillator which uses a "wave reflection" phenomenon to produce a superior support structure for a vibrating member. A capacitively coupled drive structure in an evacuated enclosure to reduce deleterious air damping is disclosed.
U.S. Pat. No. 4,445,256 to Huguenin et al. discloses a method for manufacturing piezoelectric resonator components wherein the resonator is produced using "wafer level assembly" wherein a multiplicity of resonators are formed on a large quartz wafer. This quartz wafer has been welded to a top and bottom cover which are ceramic or glass.
U.S. Pat. Nos. 4,764,244 to Chitty et al. and 4,831,304 to Dorey et al. disclose a method of making a resonator, such as a sensor, which uses micro-machining technology.
U.S. Pat. No. 4,498,344 to Dinger discloses a resonating element that is subjected directly to external strains to effect a frequency change in the resonator resulting from a strain-dependent frequency sensitivity. The support material is selected to match the thermal expansion coefficient of the resonator.
U.S. Pat. No. 4,650,346 to Tehon uses a temperature-dependent-frequency resonator element to measure temperature which is similar to a temperature dependent thickness-shear mode resonator. However, Tehon teaches a torsional electromechanical method of mechanical excitation using propagating acoustic waves.
U.S. Pat. No. 4,735,103 to Mussard et al. describes a mounting concept meant to prevent undesirable stresses from being transmitted to the resonator. The invention as disclosed in this application does not utilize force sensitivity of frequency concept as taught by Mussard et al.
U.S. Pat. No. 4,861,168 to Zeigler et al. is a thermometer based on the conventional notion of a resonator with a temperature-dependent frequency. This patent teaches capacitively coupling a rotatable resonator through the walls of the separately enclosed resonator thereby allowing the resonator to be exposed to the thermal environment without so exposing the oscillator and associated electronics. Although this patent utilizes capacitive coupling, it includes mechanical rotatable coupling and requires thermal isolation of the electronics from the resonator, neither of which is disclosed in this invention.
U.S. Pat. No. 5,048,323 to Stansfield et al. describes a gas flow correction sensor for sensing a pressure temperature function of gas flowing in a line for use in correcting the output of a volumetric flow meter connected in the line. This patent incorporates a quartz crystal tuning fork resonator as a density sensitive detector wherein the resonator is operated in the pressure and temperature ambient experienced by the measured fluid and wherein this ambient causes a well known "density perturbation" of the resonator's frequency. This patent teaches away from the pressure induced diaphragm deflection and associated capacitance and oscillator frequency change constituting the pressure detection mechanism herein disclosed.
None of the existing remote devices operate in the megahertz range which results in a significant improvement in increasing the transmission range and miniaturization of the resonator. As a result, the resonator can operate in environments where it is not possible to operate with existing systems.